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Challenge : meet the starbase (Read 1521 times)
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I Love YaBB 2!

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Challenge : meet the starbase
11/25/13 at 10:05:22
 
Hello,
 
No proper simulation there, but it setup I am having fun with : you control the probe, and try to organise rendez-vous with the starbase orbiting the moon (spend 24 hours less than 1km away from the starbace), and come back to orbit the planet.
Once you have performed it, you can try to improve on 2 parameters :
- The quicker the better.
- The les DV used the better.
 
The catch : no electronic calculator allowed. Guess and fly !
 
To make things easier, that moon is rather heavy (10% of earth mass).
 
Some help :
For those who don't master orbital flight, here are a few hints that might help you :
  • to meet the station, there are 2 steps to perfom : first move away from the planet to get into orbit around the moon. Then manage to get close enough to the starbase and stay there.
  • It will probably be easier if you might limit yourself to 4 differents burns :
    • Prograde at Apoapsis (when you are closest to the planet) : this will raise the periapsis
    • Retrograde at Apoapsis  : this will lower the periapsis
    • Prograde at Periapsis : this will lower the Apoapsis
    • Retrograde at Periapsis : this will lower the apoapsis (don't make it too strong, or you might crash in the planet).

  • To get an idea of how much DV you need to add, look at your velocity around the planet. You'll reach the escape velocity if you add prograde 0,41 times that value. So, the idea, is to add just enough to reach the moon, but less than the escape value, or you'll leave the planet's attraction. You've got time, so you are allowed to perform multiple orbits before reaching the moon.  
  • To get an idea of the moment to burn (if you wanted to reach the moon on first orbit), here are some rule of thumbs : the closer the moon's orbit form yours, the smaller the angle Moon-Planet-Probe must be (with the moon ahead of you : when you are closer you orbit more quickly, so you'll catch her up). The further you are from the moon's orbit, the closer that angle must to 116° (that angle would be the maximum)  
  • Once you are close to the moon, switch the reference to the moon (for the burn, view, and distance/speed box), and try to get into a nice orbit using the prograde/retrograde burns.
  • With the prograde/retrograde burns try to get the exact same orbit as the starbase
  • Once this is done, if you are ahead of the starbase, burn slightly prograde : you get more speed, but you will actually slow down compared to the starbase because it'll make youl orbit a bit further from the moon. Burn retrograde if you need to catch up the base.
  • Once very close to the base, you can change you reference (for the 3 panels : burn, view and distance/speed) to the starbase, and this time use the "toward/away burns"
    Don't get too close, or you'll crash...

 
Youhou !! Well done ! You have made your first rendez-vous !
 
If you want to read more, the manoeuvers performed there are close to a Hohmann transfer. Also, I might try to make tutorial using the autopilot.
 
Let me know what you thought of the little challenge !
 
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« Last Edit: 11/25/13 at 13:15:51 by flap »  
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Tony
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Re: Challenge : meet the starbase
Reply #1 - 11/25/13 at 18:21:23
 
Here are a few more tips you might not know about yet that will help you get to your starbase.
 
1. Open two Orbital Element boxes from the view menu (you can open as many of these as you like)
    Set the first one as Moon / Planet
    Set the second one as Probe / Planet.
 
2. Open a distance and velocity box from the view menu. (you can open as many of these as you like)
    Set it to Moon / Probe.
 
3.  In the Moon / Planet one, notice that the Moon's SMA is 150,000
 
4.  In the Probe / Planet one, click the Q number.  That turns the number green so it stands out better.
     When you thrust your probe, keep thrusting until Q = 150,000 for a hohman transfer.
     You still need to play with your angle.  Aim to come in behind the Moon so you are orbiting in the same direction as the Starbase.
 
5.  As you approach the Moon, keep an eye on the radial velocity.  It will go to 0 at closest approach.
 
6.  Change your thrust box to Probe / Moon. (or open an additional one.  You can open as many as you like)
 
7.  In the Probe / Moon orbital elements box, click on the e number to turn it green.
     When you arrive at your closest point (radial velocity = 0), thrust retrograde until your eccentricity = 0.  This puts you in a circular orbit.
 
8.  Switch your Probe / Earth orbital elements box to Starbase / Probe. (or open an additional one.  You can open as many as you like)
     Note the SMA.
 
9.  Thrust either prograde or retrograde to the Moon depending on if you are inside or outside the Starbase.  Thrust until either q or Q matches the Starbase's SMA.
 
10.  When you reach your closest approach to the Moon (as radial velocity in your Probe / Moon velocity box = 0), Thrust prograde or retrograde until your eccentricity gets as close to 0 as you can get it.
       You should now be in a rough circular orbit around the Moon with the same SMA as the Starbase.  
       Use imperfection to your advantage here.  If you're not perfect, you will either gain on, or receed from the Starbase with each orbit.
       Wait as many orbits as you need until you get real close to the Starbase.  (especially if you're going for the delta-v award. Then circularize your orbit.  There are two ways to do this:
       A. Burn (prograde or retrograde) at your (closest or furthest) point from the Moon until you minimize your eccentricity.
       B. Wait until you cross the 150,000 km distance.  Then burn (towards or away) until your eccentricity minimizes.  Then burn (prograde or retrograde) until your eccentricity minimizes.
 
11.  Take notes as to how much delta V you used, and at what times and in what directions.  
      Then you can use this info to create a simulation with autopilot instructions that will run automatically.  
      You can upload this file to claim your (fastest or least delta V) award!
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flap
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I Love YaBB 2!

Posts: 26
Gender: male
Re: Challenge : meet the starbase
Reply #2 - 11/25/13 at 22:13:20
 
Hey, I didn't know that you could open mutliple boxes... Useful. Also, I finally understand better how to use the orbit box.
 
Quote:
11.  Take notes as to how much delta V you used, and at what times and in what directions.  
Then you can use this info to create a simulation with autopilot instructions that will run automatically.  
You can upload this file to claim your (fastest or least delta V) award!

 
That would be cool. But while the thrust box is really convenient, it might be a bit tedious to run again the simulation and try to reproduce it with the autopilot. 2 new features would make it much easier :
- Record : Each time you press the thrust box it adds what you have done in the autopilot (3 orders : orientation, thrust start, end of thrust 1 second later)
- Replay : the ability to restart the simulation, but keeping in memory your autopilot.
 
Regarding the "replaying" point, it can easily manually done. I might soon post a tutorial explaining a simple way to do it with notepad++ and the "compare" plugin.  
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